In a typical power-electronic system, power-electronics components such as discrete or integrated (i.e. module type) semiconductor devices, inductors, resistors, capacitors and copper bus-bars are assembled in close proximity. PCB panels and control electronics are also present in all designs. During operation, these components dissipate heat of varying quantities. In addition, these components are subjected to temperatures of varying levels. The thermal management and integration concept of a drive system has to consider the occurring temperature ranges.
For power-electronic (PE) systems in the lower and medium power range, air cooling is an often used solution due to its simplicity, robustness and low investment cost. It is, however, limited in cooling performance compared to water cooling.
Another attractive cooling option is passive two-phase cooling. Here, an evaporator is in thermal contact with a heat source, typically a semiconductor module. The vaporized two-phase fluid is guided to a condenser, where the fluid returns back to liquid state, transferring the heat to ambient air. The motion of two-phase fluid is driven by gravity, pressure pulsations or capillary forces, and does not use mechanical pump. The two-phase fluid is filled at production and the cooler is hermetically closed, such that it is maintenance free over its lifetime.
Like in air cooling, in two-phase cooling the heat is ultimately transferred to air. However, the intermediate step via the two-phase fluid avoids the heat-spreading problem in classical, conduction-based air cooling (air-cooled heat sinks). Therefore, with two-phase cooling, higher cooling performance and heat flux can be achieved than with air cooling.
However, cost considerations and the challenging integration and orientation of a two-phase system into power-electronic systems restrict the application of two-phase cooling systems in power-electronic systems.